Technical Article

Vibration Sensors For Use In Condition Monitoring

May 09, 2023 by Antonio Armenta

Vibration sensors measure the mechanical vibration of an object, making it possible to monitor machines for early signs of failure to prevent costly and dangerous breakdowns.

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Vibration is an oscillatory motion that occurs in mechanical systems. Machines and structures that carry dynamic loads are subject to vibration. Examples of objects typically subjected to dynamic loads include engines, bridges, rotating machinery, and buildings.

Although the internationally recognized unit of measurement for vibration is the watts per square meter, other units are utilized, such as acceleration (meters per square second), frequency (hertz), and velocity (meters per second).


What Is Mechanical Vibration?

Mechanical vibration can occur due to internal or external factors. Internal factors are intrinsic to the conditions of the machine. Examples of internal factors are wear and tear, unbalanced forces, and resonance. Wear and tear produce vibration as high-moving parts such as gears, roller bearings, and drive belts wear down. Unbalanced forces can be caused by misaligned machine shafts or weight imbalances around a rotating axis. Finally, resonance is a phenomenon that can amplify vibration. It occurs when an object’s vibration resonates with the natural frequency of another object nearby. It can be particularly damaging due to its magnifying effects.


mechanical vibrations considered to design resilient buildings

Figure 1. Mechanical vibrations must be considered to design resilient buildings. Image used courtesy of Adobe Stock


External mechanical vibration factors include wind, traffic, and even seismic movement. In the medium-to-long term, mechanical vibration can permanently affect mechanical systems and structures' performance, reliability, and safety. Sometimes, the damage is so severe that vibration leads to total system failure. For this reason, it is vital to monitor and control vibration.


How Does a Vibration Sensor Work?

Vibration sensors are devices that can measure small, repetitive motions of an object. They allow machines to be monitored for early signs of failure and can help prevent costly and dangerous breakdowns.

In principle, vibration sensors can convert mechanical motion into electrical signals. These sensors utilize piezoelectric crystals placed between two electrodes connected to an electric circuit. A piezoelectric crystal can produce a voltage when submitted to mechanical stress and vibrations. The voltage is directly proportional to the amount of mechanical stress or vibration.


quartz commonly used piezoelectric crystal

Figure 2. Quartz is one of the most commonly used piezoelectric crystals. Image used courtesy of Adobe Stock


Vibration sensors have become essential components of predictive maintenance systems in the modern industry as part of condition monitoring. Condition monitoring consists of monitoring specific machine parameters to identify the potential for a developing fault. Vibration is among those condition parameters that, until recently, have not been as closely watched as others. In the past, accelerometers were utilized for vibration analysis, but piezoelectric vibration sensors have recently become more commonplace.

In the next sections, we will review the different types of vibration sensors available and some of the most relevant applications.


Eddy Current Sensor

Eddy currents are electrical currents induced on conductor materials by changing magnetic fields. Eddy-current-based vibration sensors consist of a coil of wire placed near the object to be measured. When that object moves, the magnetic field around the coil changes, inducing current in the coil. The resulting induced voltage is amplified and processed to calculate the object’s vibration.


eddy current vibration sensor diagram

Figure 3. Diagram of an eddy-current vibration sensor. Image used courtesy of Bestech Australia


Accelerometer Vibration Sensor

Accelerometers come in many forms. In the context of vibration sensing, these sensors determine the quantity of vibration by measuring the acceleration of an object in three dimensions, which is important for identifying the source of the vibration. Accelerometers are built using piezoelectric components and are the most commonly used form of vibration sensor.

Another form of vibration sensor is vibration meters, which measure velocity instead of acceleration.


Where Are Vibration Sensors Used?

As mentioned before, vibration sensors can be used in various applications ranging from home appliances to manufacturing equipment. Some of the most common applications include:


Motors and Gearboxes

Vibration sensors are essential for monitoring the condition of motors and gearboxes in industrial equipment. The vibration of motors and gearboxes is a common issue in industrial applications and can indicate potential problems with the equipment. In addition, vibration sensors can produce valuable information regarding early signals of wear, tear, misalignment, and imbalances. This information can be used to schedule maintenance and prevent downtime.


vibration sensor for remote condition monitoring

Figure 4. Vibration sensor for remote condition monitoring. Image used courtesy of Fluke


Rotating Equipment

Pumps, fans, and turbines are other examples of equipment subjected to high vibration levels due to constant rotation.



Industrial compressors are mechanical devices used to increase the pressure of a gas. They are widely used to power pneumatic tools and machinery and to provide compressed air for manufacturing processes. There are many industrial compressors, many of which are usually subject to high vibration levels, such as rotary screw compressors and centrifugal compressors.


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